Third generation partnership project (3GPP) mobile communication systems based on a wideband code division multiple access (WCDMA) radio access technique are widely spread all over the world. High-speed downlink packet access (HSDPA) that can be defined as a first evolutionary stage of WCDMA provides 3GPP with wireless access technique that is highly competitive in the mid-term future. However, since requirements and expectations of users and service providers are continuously increased and developments of competing radio access techniques are continuously in progress, new technical evolutions in 3GPP are required to secure competitiveness in the future.
The 3GPP launched a study project named “Evolved UTRA and UTRAN” at the end of 2004, for the purpose of developing radio transmission technique that can drastically reduce costs while providing high quality services. This 3G long-term evolution (LTE) project is in pursuit of reducing costs of users and service providers and improving service quality, as well as expanding coverage and improving system capacity. The 3G LTE defines high level requirements, such as reduction of cost per bit, increase of service availability, flexible use of frequency bands, simple structure and open interface, and proper power consumption of a user equipment.
There are one or more cells within the coverage of a base station. In addition, a plurality of user equipments can be placed within a cell. Generally, a user equipment performs random access procedure to gain access to a network. The random access procedure is accomplished through a RACH (Random Access Channel), i.e., an uplink transmission channel. The user equipment transmits an initial control message to the network through the RACH. The aim of performing the random access procedure is to obtain time synchronization between the user equipment and the network or to obtain radio resources for uplink transmission.
There are two kinds of random access procedures. In non-contention-based random access procedure, a dedicated identifier for identifying a user equipment is allocated. Therefore, random access procedure can promptly be completed since contention between user equipments does not occur. But resources for the dedicated identifier are needed. On the contrary, in contention-based random access procedure, a user equipment initiates the random access procedure without the dedicated identifier. Identifier for the user equipment is allocated during the random access procedure to resolve contention between user equipments. When the identifier for identifying the user equipment is not efficiently allocated to the user equipment, the contention may not be resolved. As a result, synchronization or uplink transmission may be delayed. Therefore, there is a need for a method of resolving contention in the contention-based random access procedure.